DNA: An Evolving Forensic Tool

DNA testing has become routine in criminal investigations, and it also has been used to demonstrate that people convicted of crimes are innocent. But its history as a forensic tool is fairly recent.

DNA testing has become routine in criminal investigations, and it also has been used to demonstrate that people convicted of crimes are innocent. But its history as a forensic tool is fairly recent.

1986 – Results of simple DNA tests are used for the first time in a criminal case in England.

1987 -- DNA is used for the first time in a criminal case in the United States in Florida. All early DNA testing was called restriction fragment length polymorphism, or RFLP, testing, which required a relatively large DNA sample and took weeks to process.

1988 – In an effort to determine if fragments of bone could be Helle Crafts', Connecticut officials have a private laboratory do DNA testing. The samples were too degraded to tell anything other than that the bone fragments were from a female.

1989 – The Connecticut Forensic Laboratory is one of the first state laboratories in the country to do polymerase chain reaction, or PCR, testing, which requires less DNA. Former lab director Elaine Pagliaro calls PCR "the biological copy machine," capable of taking a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular sequence for matching.

Early 1990s – The introduction of PCR testing leads to the next advance in DNA, known as short tandem repeats, or STR, testing. An individual inherits one copy of an STR from each parent, which may or may not have similar repeat sizes. The number of repeats in STR markers varies among individuals, which make them effective for identifying humans. Pagliaro said STR testing made it possible to make very specific matches in criminal cases, such as a one-in-a-billion match.

Early 2000s – The Connecticut Forensics Laboratory is one of four labs chosen by the FBI to do mitochondrial DNA testing, which allows scientists to extract DNA from hair or older bones or degraded DNA samples that previously they would not have been able to test. Pagliaro said if mitochondrial testing had been available back in 1988, investigators likely would have gotten more definitive results in the wood chipper case.